ANÁLISE DA PROPAGAÇÃO E MANUTENÇÃO DOS VÓRTICES GERADOS POR UM MICROBURST ESTÁTICO E ISOLADO

The Southern Brazilian region is specially affected by extreme weather events, very often intense wind gusts coming from deep convection may develop itself as a microburst producing winds higher than 100 km/h. In order to understand the physical and dynamical process evolved in this phenomena, a static and isolated microburst is produced through a Large Eddy Simulation. A quantitative analysis of propagation an maintenance of the microburst vortex ring is performed in order to understand its evolution.

Download Full-text

Large Eddy Simulation of a Vortex Ring Impacting a Bump

Advances in Applied Mathematics and Mechanics ◽

10.4208/aamm.2013.m285 ◽

2014 ◽

Vol 6 (3) ◽

pp. 261-280

Author(s):

Heng Ren ◽

Ning Zhao ◽

Xi-Yun Lu

Keyword(s):

Large Eddy Simulation ◽

Vortex Ring ◽

Three Dimensional ◽

Vortical Flow ◽

Flow State ◽

Vortical Structures ◽

Eddy Simulation ◽

Large Eddy ◽

Flow Phenomena ◽

Flow Evolution

AbstractA vortex ring impacting a three-dimensional bump is studied using large eddy simulation for a Reynolds number Re = 4 × 104 based on the initial diameter and translational speed of the vortex ring. The effects of bump height and vortex core thickness for thin and thick vortex rings on the vortical flow phenomena and the underlying physical mechanisms are investigated. Based on the analysis of the evolution of vortical structures, two typical kinds of vortical structures, i.e., the wrapping vortices and the hair-pin vortices, are identified and play an important role in the flow state evolution. The boundary vorticity flux is analyzed to reveal the mechanism of the vorticity generation on the bump surface. The circulation of the primary vortex ring reasonably elucidates some typical phases of flow evolution. Further, the analysis of turbulent kinetic energy reveals the transition from laminar to turbulent state. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the flow evolution and the flow transition to turbulent state.

Download Full-text

Large-Eddy Simulation and Particle-Image Velocimetry of single-vortex ring instabilities

2018 Fluid Dynamics Conference ◽

10.2514/6.2018-4035 ◽

2018 ◽

Author(s):

Zongxin Yu ◽

Jean-Baptiste Chapelier ◽

Carlo Scalo ◽

Pavlos Vlachos

Keyword(s):

Particle Image Velocimetry ◽

Large Eddy Simulation ◽

Vortex Ring ◽

Particle Image ◽

Single Vortex ◽

Eddy Simulation ◽

Image Velocimetry ◽

Large Eddy

Download Full-text

On the Equivalence of Two Schemes for Convective Momentum Transport

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-068.1 ◽

2012 ◽

Vol 69 (12) ◽

pp. 3491-3500 ◽

Cited By ~ 13

Author(s):

David M. Romps

Keyword(s):

Large Eddy Simulation ◽

Pressure Gradient ◽

Mass Flux ◽

Deep Convection ◽

Momentum Transport ◽

Gradient Force ◽

Pressure Gradient Force ◽

Eddy Simulation ◽

Large Eddy ◽

Convective Momentum Transport

Abstract The Gregory–Kershaw–Inness (GKI) parameterization of convective momentum transport, which has a tunable parameter C, is shown to be identical to a parameterization with no pressure gradient force and a mass flux smaller by a factor of 1 − C. Using cloud-resolving simulations, the transilient matrix for momentum is diagnosed for deep convection in radiative–convective equilibrium. Using this transilient matrix, it is shown that the GKI scheme underestimates the compensating subsidence of momentum by a factor of 1 − C, as predicted. This result is confirmed using a large-eddy simulation.

Download Full-text

Requirements for large-eddy simulation of surface wind gusts in a mountain valley

Boundary-Layer Meteorology ◽

10.1007/bf00119422 ◽

1996 ◽

Vol 80 (4) ◽

pp. 333-353 ◽

Cited By ~ 11

Author(s):

Michael J. Revell ◽

Don Purnell ◽

Michael K. Lauren

Keyword(s):

Large Eddy Simulation ◽

Surface Wind ◽

Mountain Valley ◽

Eddy Simulation ◽

Wind Gusts ◽

Large Eddy

Download Full-text

Large eddy simulation of flow around a reverse rotating propeller

Journal of Fluid Mechanics ◽

10.1017/jfm.2013.292 ◽

2013 ◽

Vol 729 ◽

pp. 151-179 ◽

Cited By ~ 21

Author(s):

Hyunchul Jang ◽

Krishnan Mahesh

Keyword(s):

Large Eddy Simulation ◽

Vortex Ring ◽

Free Stream ◽

Reverse Flow ◽

Separated Flow ◽

High Amplitude ◽

Reverse Direction ◽

Eddy Simulation ◽

Large Eddy ◽

The Impact

AbstractThis paper studies the flow around a propeller rotating in the reverse direction in a uniform free stream. Large eddy simulation is used to study this massively separated flow at a Reynolds number of 480 000 and advance ratios $J= - 0. 5$, $- 0. 7$ and $- 1. 0$. Simulations are performed on two grids; statistics of the loads and velocity field around the propeller show encouraging agreement between the two grids and with experiment. The impact of advance ratio is discussed, and a physical picture of the unsteady flow and its influence on the propeller loads is proposed. An unsteady vortex ring is formed in the vicinity of the propeller disk due to the interaction between the free stream and the reverse flow produced by the reverse rotation. The flow is separated in the blade passages; the most prominent is the separation along the sharp edge of the blade on the downstream side of the blade. This separation results in high-amplitude, transient propeller loads. Conditional averaging is used to describe the statistically relevant events that determine low- and high-amplitude thrust and side-forces. The vortex ring is closer and the reverse flow induced by propeller rotation is lower when the loads are high. The propeller loads scale with $\rho {U}^{2} $ for $J\lt - 0. 7$ and with $\rho {n}^{2} {D}^{2} $ for $J\gt - 0. 7$.

Download Full-text

Scale-Similarity Subgrid-Scale Turbulence Closure for Supercell Simulations at Kilometer-Scale Resolutions: Comparison Against a Large Eddy Simulation

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0187.1 ◽

2020 ◽

Author(s):

Shiwei Sun ◽

Bowen Zhou ◽

Ming Xue ◽

Kefeng Zhu

Keyword(s):

Large Eddy Simulation ◽

Deep Convection ◽

Eddy Diffusivity ◽

Turbulent Fluxes ◽

Subgrid Scale ◽

Diffusion Type ◽

Eddy Simulation ◽

Gradient Diffusion ◽

Large Eddy ◽

Scale Similarity

AbstractIn numerical simulations of deep convection at kilometer-scale horizontal resolutions, in-cloud subgrid-scale (SGS) turbulence plays an important role in the transport of heat, moisture and other scalars. By coarse-graining a 50 m high-resolution large-eddy simulation (LES) of an idealized supercell storm to kilometer-scale grid spacings ranging from 250 m to 4 km, the SGS fluxes of heat, moisture, cloud and precipitating water contents are diagnosed a priori. The kilometer-scale simulations are shown to be within the “gray zone” as in-cloud SGS turbulent fluxes are comparable in magnitude to the resolved fluxes at 4 km spacing, and do not become negligible until ~500 m spacing. Vertical and horizontal SGS fluxes are of comparable magnitudes, both exhibit non-local characteristics associated with deep convection as opposed to local gradient-diffusion type of turbulent mixing. As such, they are poorly parameterized by eddy-diffusivity-based closures. To improve the SGS representation of turbulent fluxes in deep convective storms, a scale-similarity LES closure is adapted to kilometer-scale simulations. The model exhibits good correlations with LES-diagnosed SGS fluxes, and is capable of representing counter-gradient fluxes. In a posteriori tests, supercell storms simulated with the refined similarity closure model at kilometer-scale resolutions show better agreement with the LES benchmark in terms of SGS fluxes than those with a turbulent-kinetic-energy-based gradient-diffusion scheme. However, it underestimates the strength of updraft, which is suggested to be a consequence of the model effective resolution being lower than the native grid resolution.

Download Full-text